Which term describes an EEG finding that is simultaneously observed across both hemispheres?

The term that best describes an EEG finding that is simultaneously observed across both hemispheres is "generalized." This term is used in electroencephalography to indicate that the activity is diffuse and affects both sides of the brain at the same time, rather than being confined to a specific area or hemisphere.

Generalized findings typically indicate a widespread and uniform distribution of electrical activity, which can be crucial in diagnosing certain conditions, such as generalized epilepsy or diffuse brain dysfunction. In contrast, localized findings would indicate activity restricted to one area of the brain, multifocal would refer to multiple distinct areas being affected, and synchronous describes the timing of the waveforms rather than their spread across the hemispheres. Thus, "generalized" is the appropriate term for findings that are bilaterally and simultaneously present.